This invention relates generally to orthopedic surgery and, in particular, to improved shoulder prostheses featuring more anatomic rotator cuff attachment geometries facilitating enhanced fixation of tendon and/or bone.
A typical proximal humeral prosthesis is depicted generally at 100 in FIG. 1, this particular drawing being taken in part from U.S. Pat. No. 5,282,865. The device includes a modular head attachment 106, though variations of such devices exist, including those without modularity, and designs incorporating different modular arrangements.
A tab 102 is provided on the lateral side of the prosthesis, as shown. The tab 104 is provided with two or more holes 106 disposed parallel to the length of the prosthesis; that is, parallel to the axis 108 of the stem 110. Although the stated purpose of the apertured tab 102 is to assist with installation of the device and to minimize rotation once installed, it is common practice in repairing a fracture to bring previously detached tendons together and suture them to this vertical tab on the lateral side of the prosthesis.
The tendons which are detached during the procedure may include the subscapularis tendon, the supraspinatus tendon, the infraspinatus tendon, and the teres minor tendon, the anatomy of each being well known, particularly to orthopedic surgeons. Since, in the case of a natural humerus, these tendons attach at different points of the bone to perform specific functions, vertically oriented tabs such as tab 102 in FIG. 1 does not adequately accommodate human anatomy.
More particularly, existing configurations are acceptable only with respect to the attachment of the posterior and anterior tendons. Since the supraspinatus tendon naturally lies flat along the top surface of the bone, the use of a vertical tab leads to an orientation which is perpendicular to the desired attachment configuration. This result, being anatomically incorrect, typically results in a reduced range of motion and strength following the procedure, particularly in initiating abduction; that is, in raising that arm. This is especially true in proximal humerus fractures known as xe2x80x98four-partxe2x80x99 fractures involving the head, shaft, greater tuberosity, and lesser tuberosity. Re-attachment to a vertical fin with sutures results in poor fixation in a non-anatomic arrangement.
The subject invention resides in a humeral prosthesis with improved anatomic attachment areas for tendon or bone. As in prior-art devices, the invention includes an elongated body having a proximal end and a distal end terminating in a stem with an axis configured for placement within an intramedullary canal of a humerus. In the preferred embodiment of the invention, however, and in contrast to existing devices, at least one set of tendon/bone attachment points are provided along a line, at least a portion of which is divergent with respect to the axis of the stem.
One or more sets of attachment points may further be provided along a line which is substantially parallel to the axis of the stem, resulting in a xe2x80x9cT,xe2x80x9d xe2x80x9cUxe2x80x9d or xe2x80x9cLxe2x80x9d configuration, including inverted versions thereof. Alternatively, attachment points having a changing degree of diversion with respect to the axis of the stem may be provided along a common, curved line. The attachment points may simply be apertures formed through the body of the implant though, in the preferred embodiment, the apertures are provided on raised tabs. An area of bone-ingrowth material may be provided adjacent to or at the attachment site, and may include a separate fastening mechanism such as a threaded hole to receive a screw, or any other alternative means operative to rigidly attach the tendon or bone to the prosthesis. A groove may also be provided in any embodiment to receive the biceps tendon. In addition, a recess may be provided to accept a tendon-bone unit such as the greater or lesser tuberosities with their respective tendons attached. Particularly with respect to fractures, including multi- and xe2x80x98four-partxe2x80x99 fractures, means specifically intended for the rigid reattachment of the greater or lesser tuberosities may be provided separately or in conjunction with other sets of reattachment configurations.